Method and apparatus for sealingly joining fuel tank sections, and fuel tanks formed thereby



nited METHOD AND APPARATUS non SEALINGLY JolNrNG FUEL TANK sncrroNs, ANDFUEL TANKS FoRMED THEREBY Billy Franklin Baumann, Northridge,

Royal Jet, Inc., Alhambra, California Application August 16, 1954,serial No. 450,004

' s claims. (C1. 22o-.80)

Calif., assigner t Calif., a corporation of factnred in at least threesections which may be nested j in a compact arrangement for shippingpurposes. After shipment to air fields in all parts of the world, thedisassembled and nested tank sections must bev assembled into thecompleted tanks, after which they are mounted beneath the wings ofaircraft in order to increase the fuel capacity thereof.

Since at least two jettis'onable fuel tanks are mounted on'an airplanefor each combat mission, and since the tanks are jettisoned when emptiedinstead of being returned to .the air field, it will be understood thatan.

enormous number of such tanks are employed in any military operationutilizing substantial numbers of airplanes. Because of the fact thatgreat numbers of fuel tanks must be assembled in the field, and becauseof the fact that the persons assembling the tanks are frequently Armypersonnel whoin certain instances are not skilled in such mechanicaloperations, it is extremely important that the circumferential jointsbetween the tank sections have only a small number of parts and becapable of rapid assembly. In spite of this requirement of speed ofassembly, however, it has in the past been conventional to employ asmany as one'hundred 4or two hundred separate parts for thecircumferential joints,` this being because the .joints are subjected tovery large vibratory and tensile'stresses when secured to theI wingsof'aircraft ily#l ing at high speeds.

In view of the above factors characteristic of the field rot"circumferential joints between aircraft fuel tank sections, it is anobject of the present invention to provide a method and apparatus forjoining cylindrical tank section ends with but a few parts and byrelatively unskilled personnel, yet which results in an extremely strongsealed joint capable of withstanding the vibratory and tensile stressesto which the tanks are subjected when mounted on thewings of high speedaircraft.

Another object of the invention is to provide a strong, sealed jointwhich is assembled without employing nuts"7 bolts or washers, therebeing only a single part to be tightened by 4the mechanic assembling thetank.

A further object of the invention is to provide a tank the sections ofwhich may be deformed in the field to provide a strong circumferentialjoint which is sealed against leakage of aircraft fuel. v

These'and other objects and advantages of the invention will be morefully set forthin the following specilication and claims considered inconnection with the attached drawing to which they relate.

l'n the drawing:

Figure 1 is a side elevational view of an aircraft fuel tank having twojoints assembled inaccordance with the present invention;

tats are` vdiscovered that the deformability,

2,832,5@3 'Patented Apr. 29, 1,95@

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Figure 2 is a transverse sectional view of the retaining or abutmentring, and illustrating the two sealing rings in position;

Figure 3 shows two cylindrical tank section ends disposed in endwiseabutment between the retaining ring of Figure 2 and an encircling girthring or strap;

Figure 4 is a section on line 4-4 of Figure 1, and illustrates thecomponents of Figure 3 after tightening of the girth ring to deform thetank section end portions;

Figure 5 is a sectional view taken along line 5-5 of Figure l andshowing the turnbuckle adapted to tighten the girth ring; and

Figure 6 illustrates an alternate form of the invention in which a boltand nut are substituted for the turnbuckle of lFigure 5. y

Broadly stated, the invention comprises the concept of joining tanksections of lightweight deformable metal, such as rolled aluminum, bydisposing them in endwise relation and applying end tension to anencircling girth strap. Preferably, an abutment ring is providedinteriorly of the tank and is so shaped that when the ends of the tanksections are deformed against it an extremely strong interlockingrelationship will result. Sealing rings, such as rubber O-rings, areplaced in positions such that the girth-tightening or deformingoperation will effect seals at the points necessary to prevent leakageof the aircraft fuel subsequently contained within the assembled tank.

Referring to the drawing, the invention is illustrated as embodied in athin-walled jettisonable aircraft fuel I tank lt) having a nose section11, a center section 12, and a tail section 13. The center section 12 isperfectly cylindrical, whereas nose section 11 and tail section 13 arestreamlined in shape although generally cylindrical at their endportions where they are joined to center section 12 by means of jointsindicated generally by the reference numeral 14. It is to be understoodthat when Vthe tank is shipped from the factory to the air field whereitis to be employed, the nose and tail sections 11 and 13 are nestedtogether within center section 12, so that a compact unit results. Thejoints 14 beingv identical in construction, only the one between centersection 12 and tail section 13.will be described.

Referring particularly to Figures 2-4, the components of each joint 14are seen to comprise a retaining or abutment ring 16, a girth ring orstrap 17, and a pair of sealing rings 18. Retaining ring 16 ispreferably a rolled section of high strength aluminum alloy, whereasgirth ring 17 is a flexible thin steel band or strip having a hightensile strength. Sealing rings 18 are preferably large diameter O-ringsformed of rubber orthe like, and the skin of each tank section 11-13 isrolled aluminum or similar metal capable of ready deformation. It hasbeen represented by ductility, malleability, etc., of the skin sectionsis such that when their cylindrical end portions are necked down I upontightening of the encircling girth ring 17 no crimping or crinkling willoccur, the necking being instead highly uniform and operating to providea sealed Vjoint having a very high tensile strength.

Retaining or abutment ring 16 is preferably shaped with a pair ofinwardly extending edge tianges 21 which impart strength to the ring,the flanges merging in each instance with cylindrical shoulder sections22 adapted to abut the interior surfaces of skin sections 12 and 131.

The cylindrical shoulder sections 22 merge at their edges oppositeflanges 21 with frusto-conical walls 23 which in turn lead tocylindrical portions 24 corresponding to shoulder sections 22 but oflesser diameter, it being understood that the shoulder sections 22, theconical walls 23 and the cylindrical portions 24 are co-axial with tanksctions 12 and 13. At their edges remote from frusto-conical walls 23,cylindrical portions 24 merge with portions" 26 which curve inwardly toprovide seats forthe 0,-rings 18. The portions 26 are generally adjacenteach other and are separated by a raised ridge 27, the crest of ridge 27being preferably 'at the same-radial lpositionpafsthe cylindricalportions y24.

it is to be understood that the described integral and symmetricalconstruction of ri'ngf 16rcsults in ai peripheral channel adapted tovreceive the tankrsection end portions, the channel being defined by1elementsror'portions 23, 24, '26 and27. Furthermore, the Walls or'portionsV 22 and 23 form together shoulderelements such that ,theneckeddown tank section endsrnay riot be drawnther'epast. Y

Girth ring or strap 17 is a thin at handhaving internal beads 28 on itsedges, the width of thebandbeing'such vthat vbeads 28 are disposedradially outwardly of the cylindricalportions 24 of abutment ring 1.6.As illustrated in vFigure 5, the ends of girth ring 17 are bent overkand lwelded 4to form loops 29 which pass over theends of asuitableturnbuckle 30. vThe nut portion 31 of turn- Vbuckle 30 seatsrotatably in a fitting 32,V the lowerportion of the latter being weldedtoathin plate 33 adapted Ito' .b e insert ed beneath the ends of girthring 17 in order 4to hold theturnbuckle in position during thetightening operation. The operation/of the turnbuckle 30 is such thattheloopedstrap ends 29 will be drawn toward eachother.toeffecttensioning of theV strap upon rotation of ,nut`31 inafgiven'direction and by a wrench or the like.

`Referring toFigure 6, the turnbtickle 30 may -be replacedbyanutjandfbolt connection if' desired, one end of the strap 17Vbeing-looped around the nut 34 and the other ystrap end being loopedaround a washer 36. bolt 37 is inserted through holes in one strap endand its washer 36, and is threaded into and through the nut 34 and holeslin the other. strap end, so that turning of the bolt operates lto drawthe strap ends together as desired.

vInpi'acticing the method of the invention, the skin sections"121`arid 13 vare disposedv in coaxial endwise relation and girth `ringf'17 is'placed therearonnd, both. the vgirth'ring arid'theskin'end portionsbeing radially adjacent peripherally'channelled retaining or abutmentring 16. It lis thenrnerely necessary to reduce the diameter of girthring 17 lby'A drawing its ends together so that the resultant pressure,operates to neck down the end portions of skin sections 12 and 13 -intothe peripheral v channel 4in abutment lring 1 6, seals being Vproyidedprevent lleakage of fluid from the where necessaryto completed tank.

More specifically vand.'with thefapparatus illustrated in Figures 2-5 ofthe drawing,' the'invention is practiced b yvseating the O7rings 18.in''groove portions 26 of abut- Yment ring 16, vand then" placing theV skinsections 12 and 13'in endwise abutment sothat the line of abutment isAradially 'adjacent theraisedridge 27. `The O-rings 18 "are Vof such acrossfsectiorial diameterthat they engage both the portions 26 and vtheskinsections, the skin sections being also engagedby the cylindricalshoulder sections 22. G irth ring 17 `is' thenniounted .in position Abyslipping thesarne over tail" section 13,;theiiitting32 beingfinsertedbeneath nut to provide ai journal there- -for as previously indicated. fT 'h e lo c ationV ofjgirthring -17 is s'uch that its beads '28aregenerallyradially outwardly of cylindricalpottions"24'ofgabutmentring 16.

After the parts are thusi assembled ,initially and as shown in Figure 3,thenut 31 is turned `in a direction effectingA drawing of7looped Yend`portionsl 29 of girth ring 17 toward each other, Whichdecreases thediameter cylindrical portions 24 of abutment ring 16, the girth ringabutment element a 17 then being approximately ush lwith the skinsections 12 and 13 so that the resulting joint 14 is externally cleanand smooth and provides substantially no resistance to air ow.

After the joint has been completed as shown in Figure 4, the O-rings 1Sare sufficiently deformed to prevent anyieakage of-iiuid through thejoints. Furthermore, thejoint has very high tensile strength since anyattempt to draw the skin section 12 away from skin section i3 will beresisted by the action of bends 28 which seat in channels 38.Additionally, should the skin sec- `tions"12 and 13 be drawn somewhatapart due tothe presence of extremely'high tensile stresses, thevchannels 38 willcorne into abutment vwith frustO-conical walls 23 whichwill operate to furtlieriiicrease the resistance of the joint tobreaking. v

In the described manner, an extremely strong and aerodynami callycleansealed joint bas--been1providedwith Aa minimum number of parts and byrncrely turning the n ut 31of turnbuckle 30. This is ,to be comparedwith conventional fuel tank joints vwhich comprise-hundreds of nuts,bolts, sealing rings, washers, etc.yet which are ,-aerodynamicallyilesssatisfactory, and in many instances have'lower tensile strengths,`thanthe present joint.

.While the Vrparticular method andv apparatus herein shown and describedin detail are fullyicapableofattaining the ,objects and providing.before stated, itistto 'beruiiderstood lthat .they ,are` merely theadvantages hereinillustrative of the presently preferred embodiments ofIfclaim: ,1. Ajoirit for ajettisonable aircraft fuel tank formed 'ofthinwlalledjrolled alumintim,. s aid tank comprising a :plurality ofysections having cylindrical end portions which arebutt'ed against eachother, whic h comprises an annular abut-ment elementmounted in .saidtankradially inwardly h'otsaid butted end portions, said abutment elementhav- `inga relativly Wide shallow peripheral .channel the botisformedwith a groove adjacent each contact of said b utted end portions,an in each of .said grooves, and a tiexible steel Vgirth stripmountedradiallyoutvvardlyof said channel bottom YWall landencompassing saidline ofcontactof said butted end portions, said irth strip beingprovidedtom fvvall of which iiith means: perr'nittingY manual reductionin Y thediai'neter ducedinpdiemeisr by anemounfiifviicien't to neckrlown saidbutted end" portions intosaid ,peripheral channel, s aidneckirig downresulting'in-dcformation vof saidQ-rings into sealing-engagementwithsaid d end portions and also resultingin interlocking .of said end.portions with the shoulder portions of said abutment element on eachside of said channel.

n 2. The invention as clairnediri claim v 1, inwhich said .girth stri-pis -provided on eaehjof its edgeswith an inyternal bead or ridge.

of the girth ring. vAs turning of the nut 31`progres'ses,

'the vcylindrical end portions of skin sections 1 2 -`andi-3fare-reduced in ydiameter orf-necked ov/tn, without crimp- :ing orbuckling, to effect deformation of O-rings 18 as .the channels .3,8 taref defermed tinto engagement `V :with

adaptedtn bridgek the rim edges lofsairl .tubular sections,

3. A pair of nestingrings adapted to join together in -.a;`fifliidt`i.si1t fi1snnr.the abilities rim edges of Sheetmetel itubular sections of ajettisonable fuel tank or the like "aerodynamicaily contoured structure,said rings inciudin g at iighstrength relatively wideinner ring havinga' desnugly beneath the Aadjaceiibeciges of tubular sections pressedcentral area and lateralrim,edgesadapted to tit with said tube sec onrims inV close proximity .opposite said depressedcentral area` of saidring, a relatively.. narrow ,outer ,ringof adjustable .circumferentiallength 'and means for plainggsaid'outer-rim in tension to Vreduce the-circumferentialvlength thereof andneck down the trims of..s aid-tubular sections into therdeprcssedarea of ,Said inner firing therebylocking said' Sections rigidly vassembled, said outer ring being flatand-itstouterssurface lying substantially ush with the adjacent surfaceareas of said tubular sections in the assembled position of said ringsto provide a substantially unbroken aerodynamic exterior surface fromend to end of the rigidly joined tubular sections, and the oppositelateral edges of said outer ring being -reversely bent inwardly againstthe inner ysurface of said ring to provide beads projecting inwardly andeffective upon the tensioning of the outer ring to form interlockinggrooves in the underlying rim edge portions of said tubular sections.

UNITED STATES PATENTS -Hahn Apr. 10, 1906 Hahn Sept. 25, 1906 Avery n-May 13, 1919 Hall July 31, 1928 lJensen Dec. 31, 1935 Twaits July 19,1938 Maier 20, 1951 Kanode et al Sept. 29, 1953 Brown Aug. 10, 1954Moore .Tune 19, 1956

